1. Field of the Invention
The present invention relates to a control information processing method, and more particularly, to a method of processing control information in a mobile communication system. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for preventing a user equipment from standing by unnecessarily.
2. Discussion of the Related Art
FIG. 1 is a block diagram of a network structure of UMTS (universal mobile telecommunications system).
Referring to FIG. 1, a universal mobile telecommunications system (hereinafter abbreviated UMTS) mainly includes a user equipment (hereinafter abbreviated UE), a UMTS terrestrial radio access network (hereinafter abbreviated UTRAN) and a core network (hereinafter abbreviated CN).
The UTRAN includes at least one radio network sub-system (hereinafter abbreviated RNS). And, the RNS includes one radio network controller (hereinafter abbreviated RNC) and at least one base station (hereinafter called Node B) managed by the RNC. And, at least one or more cells exist in one Node B.
FIG. 2 is a diagram of architecture of a radio protocol used for UMTS.
Referring to FIG. 2, radio protocol layers exist as pairs in both UE and UTRAN to take charge of data transmission in a radio section.
The respective radio protocol layers are explained as follows.
First of all, a physical layer PHY, which is a first layer, plays a role in transferring data to a radio section using various radio transfer techniques. The physical layer PHY is connected to a layer MAC as an upper layer via transport channels. And, the transport channels are mainly classified into dedicated transport channels and common transport channels according to whether the corresponding channel is shared or not.
A second layer includes MAC, RLC, PDCP and BMC layers.
First of all, a MAC layer plays a role in mapping various logical channels to various transport channels, respectively and also performs a function of logical channel multiplexing that plays a role in mapping various logical channels to one transport channel. The MAC layer is connected to an RLC layer of an upper layer via a logical channel. And, the logical channel is mainly classified into a control channel for transferring information of a control plane and a traffic channel for transferring information of a user plane according to a type of information that is transferred.
A radio link control (hereinafter abbreviated RLC) layer is responsible for guaranteeing a quality of service (hereinafter abbreviated QoS) of each radio bearer and also takes charge of a transfer of corresponding data. The RLC leaves one independent RLC entity at each RB to guarantee an intrinsic QoS of RB. The RLC offers three kinds of RLC modes including a transparent mode (hereinafter abbreviated TM), an unacknowledged mode (hereinafter abbreviated UM) and an acknowledged mode (hereinafter abbreviated AM) to support various QoS. And, the RLC plays a role in adjusting a data size to enable a lower layer to transfer data to a radio section. For this, the RLC plays a role in segmenting and concatenating data received from an upper layer.
A PDCP layer is placed above the RLC layer and plays a role in transferring data, which is transferred using an IP packet such as an IPv4 and an IPv6, efficiently in a radio section having a relatively small bandwidth. For this, the PDCP layer performs a header compression function, by which information mandatory for a header of data is transferred to raise transport efficiency in a radio section. Since header compression is a basic function of the PDCP layer, the PDCP layer exists in a packet service domain (hereinafter abbreviated PS domain) only. And, one PDCP entity exists for each RB to provide an effective header compression function to each PS service.
In the second layer, a BMC (broadcast/multicast control) layer is provided above the RLC layer. The BMC layer schedules a cell broadcast message and performs broadcasting to UEs located in a specific cell.
A radio resource control (hereinafter abbreviated RRC) layer located in a lowest part of a third layer is defined in a control plane only. The RRC layer controls parameters of the first and second layers to be associated with establishment, re-configuration and release of RBs and takes charge of controlling logical, transport and physical channels. In this case, the RB means a logical path provided by the first and second layers of a radio protocol for data transfer between UE and UTRAN. And, RB establishment means a process of regulating characteristics of radio protocol layers and channels to offer a specific service and establishing specific parameters and operational methods. When an RRC layer of a specific UE and to an RRC layer of UTRAN are connected together to exchange RRC messages with each other, the corresponding UE lies in an RRC connected state. IF they are not connected together, the corresponding UE lies in an idle state.
The RLC layer is further explained in detail as follows.
First of all, basic functions of the RLC layer are a QoS guarantee of each RB and a corresponding data transfer. Since an RB service is a service that the second layer provides to an upper layer, the entire second layer has influence on QoS. And, the RLC has the greatest influence. The RLC leaves an independent RLC entity at each RB to guarantee the intrinsic QoS of RB and offers three kinds of RLC modes of TM, UM and AM. Since the three RLC modes differ from one another in QoS supported by each of the TM. UM and AM, their operational methods are different from one another as well as their detailed functions. So, the RLC needs to be looked into according to its operational mode.
TM RLC is a mode that any overhead is not attached to RLC service data unit (hereinafter abbreviated SDU) delivered from a higher layer in configuring RLC protocol data unit (hereinafter abbreviated PDU). In particular, since an RLC transmits SDU transparently, it is called TM RLC. Due to such a characteristic, TM RLC plays the following roles in user and control planes. In the user plane, since data processing time within RLC is short, TM RLC performs a real-time circuit data transfer of a voice or streaming in a circuit service domain (hereinafter abbreviated ‘CS domain’). Meanwhile, in the control plane, since there is no overhead within RLC, the RLC is responsible for a transmission of an RRC message from an unspecific UE in case of an uplink or a transmission of an RRC message broadcast to all UEs within a cell in case of a downlink.
Unlike the transparent mode, a mode of adding an overhead in RLC is called a non-transparent mode that is classified into an unacknowledged mode (UM) and an acknowledged mode (AM). By attaching a PDU header including a sequence number (hereinafter abbreviated SN) to each PDU to transfer, UM RLC enables a receiving side to know which PDU is lost in the course of transmission.
In aspect of a transmitting side RLC, a transmitting side operating in UM does not check whether a receiving side receives a corresponding PDU correctly. So, the transmitting side does not transmit a PDU that was transmitted once. In an aspect of a receiving side RLC operating in UM, a receiving side checks which PDU is lost through a sequence number of a received PDU. The receiving side does not further expect a reception of the PDU decided as lost and immediately delivers the successfully received SDU to an upper layer. For instance, if a specific UM RLC receives an RLC PDU having a sequence number of ‘6’ after having received an RLC PDU having a sequence number of ‘3’, the corresponding UM RLC decides that a reception of an RLC PDU having a sequence number of ‘4’ or ‘5’ fails and does not expect a further reception of the PDUs any more.
Owing to this function, the UM RLC is mainly responsible for a transmission of real-time packet data such as a broadcast/multicast data and a voice (e.g., VoIP) or streaming of a packet service domain (hereinafter abbreviated PS domain) in a user plane or a transmission of an RRC message needing no acknowledgement among RRC messages transmitted to a specific UE or a specific UE group within a cell in a control plane.
Like the UM RLC, an AM RLC as one of the non-transparent modes configures a PDU by attaching a PDU header including an SN thereto. Yet, the AM RLC differs from the UM RLC in that a receiving side makes acknowledgement to a PDU transmitted by a transmitting side. The reason why the AM RLC of the receiving side makes acknowledgement is because the receiving side can make a request for a retransmission of a missing PDU by the transmitting side. And, this retransmission function is the most outstanding feature of the AM RLC. So, the object of the AM RLC is to guarantee an error-free data transmission through the retransmission. Owing to this object, the AM RLC mainly takes charge of a transmission of non-real-time packet data such as TCP/IP of PS domain in a user plane.
The UM RLC is explained in detail as follows.
First of all, the UM RLC establishes and manages the following environmental variables.
First of all, VR(US) indicates a next reception number. This value means a value right next to an SN value of a last received RLC PDU. Namely, if an SN value of ‘x’ is received, VR(US) is set to ‘x+1’.
In case of receiving RLC SDUs (service data units) from an upper layer (e.g., an upper layer of UM RLC), a UM RLC of a transmitting side generates an RLC PDU by adjusting the received RLC SDUs into a suitable size by segmentation and concatenation and then delivers the generated RLC PDU to a lower layer (e.g., a lower layer of the UM RLC). And, the UM RLC includes a length indicator (hereinafter abbreviated LI), which indicates a position of a boundary of RLC SDU within the RLC PDU, in order to enable a receiving side to recover the RLC SDUs from the RLC PDU.
In this case, a sequence number SN is represented as 7 bits. By representing the SN in a simple from, it is able to raise a transport efficiency of data to be delivered in a manner of reducing a header part from each RLC PDU. Hence, sequence numbers substantially transferred by being included in the RLC PDU are values belonging to a range between 0-127. So, the transmitting side sequentially assigns sequence numbers to the respective RLC PDUs from zero to use and then assigns sequence numbers from zero to reuse after assigning 127. Like this, a case that a sequence number starts to be reused from such a lower value as zero from a higher value of ‘127’ can be regarded as a case that ‘wrap-around’ has occurred. Hence, RLC PDUs after the occurrence of ‘wrap-around’ are the RLC PDUs that must be delivered behind RLC PDUs prior to the occurrence of ‘wrap-around’.
The receiving side always checks the SN of the received RLC PDU. If the SN of the received RLC PDU is smaller than that of the last received RLC PDU, the receiving side decides that ‘wrap-around’ has occurred. And, the entire RLC PDUs received after the ‘wrap-around’ occurrence are regarded as RLC PDUs generated behind the previously received RLC PDU.
FIG. 3 is a flowchart of a process for receiving RLC PDU from a lower layer in a UM RLC operation of a receiving side according to a related art.
Referring to FIG. 3, a receiving side receives an RLC PDU having an SN value (S300).
Subsequently, VR(US) is reset to correspond to the SN value of the received RLC PDU (S301).
If an updated width of the VR(US) value is not ‘1’ in the step S301, it is decided that there exists a lost RLC PDU (S302). RLC SDUs associated with the RLC PDUs decided as lost are then deleted (S303).
If an updated width of the VR(US) value is ‘1’, the following steps are executed.
First of all, after a recovery process has been carried out using the successfully received RLC PDUs, successfully recovered RLC SDUs are delivered to an upper layer of RLC (S304).
After the delivery (S304), the whole process is ended (S305).
An RRC state and connection method of a UE are explained in detail as follows.
First of all, an RRC state means whether an RRC of UE is in a logical connection to an RRC of UTRAN. If the RRC of the UE is in the logical connection to the RRC of the UTRAN, it is called an RRC connected state. Otherwise, it is called an RRC idle state.
Since there exists an RRC connection for a UE in an RRC connected state, a UTRAN is able to recognize an existence of the corresponding UE by a cell level. Hence, the UTRAN is able to effectively control the UE. Yet, a UTRAN is unable to recognize an existence of a UE in an RRC idle state. A core network (hereinafter abbreviated CN) manages the corresponding UE by a location area level or a routing area level that is an area unit greater than a cell. In particular, an existence or non-existence of an UE in an RRC idle state can be just recognized by a large area unit. And, the UE in the RRC idle state has to enter an RRC connected state to receive a general mobile communication service such as a voice and data.
When a user turns on a power of UE for the first time, the UE preferentially makes a search for a suitable cell and then stays in an RRC idle state at the corresponding cell. The UE in the RRC idle state establishes an RRC connection with an RRC of UTRAN through an RRC connection procedure if necessary for the RRC connection. The UE then makes a transition to an RRC connected state.
There are several cases for a UE in an RRC idle state to establish an RRC connection. For instance, the RRC connection is established if an uplink data transport is needed due to a user's attempt to make a call or the like. For another instance, the RRC connection is established if a paging message is received from UTRAN.
In order for a UE in an RRC idle state to establish an RRC connection with UTRAN, the above-explained RRC connection procedure needs to be executed.
The RRC connection procedure mainly consists of the three steps of an RRC connection request message transmission to a UTRAN from a UE, an RRC connection setup message transmission to the UE from the UTRAN and an RRC connection setup complete message transmission to the UTRAN from the UE. This RRC connection procedure is shown in FIG. 4.
FIG. 4 shows a flowchart of an RRC connection procedure according to a related art.
Referring to FIG. 4, an RRC connection request step (S401) is explained as follows.
First of all, if a UE in an RRC idle state attempts to establish an RRC connection due to a calling trial, a response to a paging of a UTRAN or the like, the UE preferentially sends an RRC connection request message to the UTRAN.
In this case, the RRC connection request message contains an initial UE identity, an RRC connection establishment cause and the like.
The initial UE identity is a unique identity of the UE and enables the corresponding UE to be globally identified regardless of the UE's location. And, there are various kinds of the RRC connection establishment causes such as a calling trial, a response to a paging and the like.
The UE drives a timer as soon as transmits the RRC connection request message. The UE retransmits the RRC connection request message unless receiving an RRC connection setup message or an RRC connection reject message from the UTRAN until the timer expires. IN this case, a maximum transmission count of the RRC connection message is limited to a specific value.
An RRC connection setup step (S402) is explained as follows.
The UE having received the RRC connection request message accepts an RRC connection request made by the UE if radio resources are sufficient. The UE then transmits an RRC connection setup message as a response message to the UE. In this case, the RRC connection setup message is transmitted by including a radio network temporary identity (hereinafter abbreviated RNTI), radio bearer setup information and the like together with the initial UE identity. And, the radio network temporary identity is a UE identity that enables the UTRAN to identify the UE in the RRC connected state. The identity is used only if there exists an RRC connection. And, the identity is used within the UTRAN only.
After the RRC connection has been set up, the UE communicates with the UTRAN using the radio network temporary identity instead of using the initial UE identity. If the initial UE identity, which is the unique identity of the UE, is frequently used, it may be drained away. So, the initial UE identity is temporarily used in the RRC connection procedure. Thereafter, the radio network temporary identity is used.
And, an RRC connection setup complete step (S403) is explained as follows.
First of all, the UE having received the RRC connection setup message checks whether the received message is a message supposed to be sent to the UE itself in a manner of comparing the initial UE identity included in the message to its identity.
If the message is the message supposed to be sent to the UE itself as a result of the check, the UE stores the radio network temporary identity assigned by the UTRAN and then transmits an RRC connection setup complete message to the UTRAN using the stored radio network temporary identity. In this case, UE capability information and the like are included in the RRC connection setup complete message.
In case of transmitting the RRC connection message successfully, the UE establishes the RRC connection with the UTRAN for the first time and then makes a transition to an RRC connected state.
Meanwhile, the RRC connection request message is transmitted on a random access channel (hereinafter abbreviated RACH), whereas the RRC connection setup message is transmitted on a forward access channel (hereinafter abbreviated FACH).
However, a network is unable to recognize an existence of the UE until the RRC connection setup is completed. So, the UE sends the RRC connection request message as a first message using the RACH shared by all UEs. And, the RACH is delivered to a connection management end of the network via a logical channel called a common control channel (hereinafter abbreviated CCCH) shared by the entire UEs. Likewise, a first message delivered to the UE from the network is delivered on a channel received by the entire UEs in common. Moreover, since a connection setup method and channel information corresponding to the UE only are included in the RRC connection setup message as the first message, the network is able to deliver the message to the corresponding UE via a common channel only until the UE receives the RRC connection setup message. In this case, the RRC connection setup message is delivered on CCCH. And, this message is transmitted in a UM RLC mode.